PubChem, released in 2004, provides information on the biological activities of small molecules.

PubChem is organized as three linked databases within the NCBI's
Entrez information retrieval system. These are PubChem Substance, PubChem Compound, and PubChem BioAssay. PubChem also provides a fast chemical structure similarity search tool. More information about using each component database may be found using the links in the PubChem homepage.